Avoid KeyError when unregistering comms

Author: impact27

ipykernel/comm/comm.py

@@ -73,7 +73,7 @@ def _publish_msg(self, msg_type, data=None, metadata=None, buffers=None, **keys)
 
     def __del__(self):
         """trigger close on gc"""
-        self.close()
+        self.close(deleting=True)
 
     # publishing messages
 
@@ -98,7 +98,7 @@ def open(self, data=None, metadata=None, buffers=None):
             comm_manager.unregister_comm(self)
             raise
 
-    def close(self, data=None, metadata=None, buffers=None):
+    def close(self, data=None, metadata=None, buffers=None, deleting=False):
         """Close the frontend-side version of this comm"""
         if self._closed:
             # only close once
@@ -113,7 +113,9 @@ def close(self, data=None, metadata=None, buffers=None):
         self._publish_msg('comm_close',
             data=data, metadata=metadata, buffers=buffers,
         )
-        self.kernel.comm_manager.unregister_comm(self)
+        if not deleting:
+            # If deleting, the comm can't be registered
+            self.kernel.comm_manager.unregister_comm(self)
 
     def send(self, data=None, metadata=None, buffers=None):
         """Send a message to the frontend-side version of this comm"""